DENVER — Voters in Boulder, Colo., will decide Tuesday whether the city will become the first in the nation to impose a “carbon tax” on homeowners and businesses to fund efforts to reduce emissions that cause global warming.

If approved, the ballot measure would tax electricity usage and add about $16-$20 a year to the average residential electric bill. Businesses would pay an additional $46 a year on average, and industries an extra $3,226, according to Yael Gichon of Boulder’s environmental affairs office. The tax could raise $860,000 in the first year.

Gichon and Matt Baker, director of Environment Colorado, a Denver-based environmental group, say that if the measure passes, it will mark the first time a U.S. city has voted in favor of a carbon tax to combat global warming.

The levy is called a carbon tax because most electricity in the USA is produced by burning coal and natural gas, which emit carbon dioxide that contributes to global warming.

Climate Smart, a local group that supports the tax, estimates the average monthly residential electric bill of $63 would increase $1.38, or 2.2%. A medium-size office building would rise $33, or 0.6%.

Boulder, one of the state’s most liberal communities, has a long history of environmental activism, such as preserving open space, recycling and encouraging use of public transit. The town of about 92,000 residents is home to the University of Colorado and the National Center for Atmospheric Research. “We have probably more climate scientists living in Boulder than any other city in the world,” Mayor Mark Ruzzin says.

The City Council authorized the ballot measure to fund a city plan to reduce greenhouse emissions 7% below 1990 levels. To accomplish that, Boulder would have to cut emissions 24% by 2012. About half of the city’s emissions are attributed to burning fossil fuels for electricity.

Four years ago, the city adopted emission targets set by the 1997 Kyoto Protocol, an international agreement the United States has not ratified, to reduce greenhouse gases such as carbon dioxide.

“There is a strong environmental ethic in Boulder,” Ruzzin says. “People are looking to do the right thing, and the climate action plan gets us down that road.”

No group has organized in the city to oppose the tax measure, and even the Boulder Chamber of Commerce has endorsed it. Climate Smart expects to spend about $8,000 on yard signs and “a few newspaper ads,” volunteer Ken Regelson says.

Gichon says the tax would fund efforts to increase energy efficiency, spur the use of renewable energy such as wind and solar power, and encourage residents to drive less. The tax also would fund city-sponsored energy audits for residences, and educational programs on utility-sponsored rebates for installing energy-efficient appliances, light fixtures and insulation.

Many states have mandated special charges on electric bills to fund energy-efficiency and renewable-energy programs. And some city-owned utilities, including Fort Collins, Colo., have raised rates to pay for renewable-energy programs.